The proposed research will examine two distinct measures of inhibitory control, sensory filtering and executive function, to determine their relationship to specific symptoms of PTSD (hypervigilance and re- experiencing) and to each other. It is hypothesized that cognitive deficits in executive function may relate to specific symptoms of PTSD and to a physiological deficit, impaired sensory filtering during stress. If obtained, this association would lend support to a model of reduced inhibitory control contributing to specific symptoms of PTSD. This proposed investigation will encompass three related studies. In the first study, sensory filtering will be assessed during baseline and stressor conditions using P50 suppression, an event- related potential measure indexing sensory filtering that has demonstrated impairment in PTSD in several published studies. The second study employs a behavioral task, the Attentional Network Task (ANT), shown to assess three attentional networks: alerting, orienting and executive function. Correlation between executive function, P50 suppression and PTSD symptoms will be assessed. The third study will examine brain activation patterns in subjects undergoing fMRI imaging (BOLD) during the attentional network task. [unreadable] [unreadable] [unreadable]